Mosquitos on the Move USA

Latest Developments

This past week at opposite ends of the country there was an expansion of the domain of mosquito species known to carry diseases infectious to humans. In Nevada (specifically Clark County, which includes Las Vegas) the Aedes aegypti mosquito was recorded for the first time, while in Connecticut the Aedes albopictus boundary has moved north, and the mosquito population is now stabilized in the state.

Changing environmental conditions have helped further the spread of these mosquito species. The lower mean average winter temperature has allowed Aedes albopictus to become established in Connecticut. The appearance of Aedes aegypti in Nevada was greeted more with expectation than surprise, given it is found in contiguous states (California and Arizona) and is easily transported by human activity (cars, trucks, produce shipping).

Michael Osterholm and Mark Olshaker in the 2017 book, Deadliest Enemy, call mosquitoes “public enemy number one.” They review the list of a major diseases – yellow fever, dengue, chikungunya, Zika – and the role of mosquitoes in transmitting them:

“All of these viruses share the Aedes aegypti as the primary vector. Its rural cousin Aedes albopictus – aka the Asian tiger mosquito – is starting to adapt to some of its habitats and has become a secondary vector....There is no magic bullet in controlling Aedes aegypti and Aedes albopictus. Studies have confirmed our conviction that good vector control is a complex science involving not only eliminating adult mosquitoes, but also reducing sources and using larvicide. We have also noted that there is no development of a new, safe, and effective insecticide to replace DDT.”

Each of these diseases have recently been covered and described by Ascel Bio (20170430 Zika SitRep, 20170417 Brazil Yellow Fever SitRep, 20170320 Brazil Yellow Fever SitRep, 20170228 Brazil Yellow Fever SitRep, 20170216 USA Zika SitRep, 20161204 Zika Alert USA...). While none of these diseases are currently endemic in the United States, even a small outbreak of one can have outsize effects on social behavior and public response; plus, changing temperature patterns will continue to push these mosquitos into newly habitable territories. More cities in the United States, as in Europe and elsewhere, will need to prioritize funding for mosquito eradication and education materials. A case of Zika in a city such as Las Vegas might lead to travel alerts from the CDC, prompting a decrease in tourism to a highly popular destination. Connecticut, which operates with a highly distributed form of governance, will need to scale up its vector surveillance efforts.

As governments begin to react to the spread of mosquito vectors into new territories, doctors and other diagnosticians will need to be aware of the novel threats they pose. This will include an understanding of each virus’s clinical manifestation, an awareness of the current seasonal and epidemiologic trends, and the availability of diagnostics to test for the disease.

Common Symptoms of 3 Mosquito-borne Diseases

Dengue

Zika

Chikungunya

Severe headache

Severe eye pain

Joint pain

Muscle and/or bone pain

Rash

Mild bleeding

Low white cell count

Fever

Rash

Headache

Joint pain

Conjunctivitis

Muscle pain

Fever

Joing pain

Headache

Muscle pain

Joint swelling

Rash

Source: CDC

Seasonal Trends

In the United States, as in much of the Northern Hemisphere, mosquito-borne infections tend to peak in the late summer and fall. As shown in the forecast below, dengue case counts in the United States are very low, with reported averages of less than 1 case per week even during peak season between July and October.

Status of Diagnostics

Diagnostics play an important role in the recognition of a specific virus and proper treatment. Currently, testing for dengue, chikungunya, and Zika can all be done by state health departments and the CDC. However, commercially available diagnostic kits and assays are unavailable for Zika, and non-FDA-approved for chikungunya. Dengue is the only virus with an FDA-approved commercially available kit. The further spread of these mosquito-borne illnesses into the US, and the increased recognition of these diseases as critical threats to human health worldwide, will likely drive the innovation and approval of new diagnostic kits.

Conclusion

As the Aedes aegypti and albopictus mosquitoes cover new ground in the United States, it will be important for federal, state, and local health departments to adopt a forward-thinking and adaptable approach to dealing with new diseases. Emergency funding sources will need to be in place in the event of an outbreak, and laboratory capacity to test for these pathogens will be important to ensuring diagnosis and response. In major cities, public education campaigns can help reduce the impact of intense media coverage on social behavior, such as tourism hesitancy. And, as always, the public can support the effort to minimize risk by removing breeding spots for mosquitoes and wearing insect repellent during peak season.